one vented fixture in whole house?

I've just bought a very modest, two-bedroom ranch built in '58. There was no shower in the only bathroom, just a cast iron tub in good shape. The room is now gutted and a carpenter will hang cement board and other wall board when the wiring and plumbing are done. An electrician did the wiring yesterday. I planned to redo the plumbing as needed. So far I've taken out rusty iron drain and supply pipes to sink. I cut off iron vent pipe that goes from near sink to roof. In the process I dislodged it from the roof and that awaits repair with pvc and a new roof piece. Today I was mulling the vent issue relative to bracing the wall where a new wall mounted sink will go. I decided to figure out where the other vent stacks were. There are none. That 1 1/4 pipe that connected to sink drain and no where else, is the only thing going through the roof other than the furnace vent. There is no typical 4" waste vent anywhere. The basement is unfinished and I can see all the plumbing. What now? Will it take a plumber to correct this? Or am I mistaken that each fixture needs to connect to the main vent? I will not live here until bathroom project is done, and water is turned off, so I don't know about drain issues relative to venting.
New here. Thanks for any help! Joni

EVERY fixture does need a vent, but there are many ways of doing that, so you may not be interpreting your system properly. It may take a plumber to look at it and decide if they is a deficiency somewhere.

Thank you for replying. I wrote prematurely and in a panic, and since I've studied the pipes better I see how it works for this little house with few fixtures, mostly quite close together. I will replace the 1 1/4 vent with 1 1/2, and when I remodel the kitchen I may choose to add a vent on that side of the house.

I still need to figure out how to run the vent through the wall w/o compromising the studs which will bear the weight of the wall mounted sink. Any suggestions?